Where did the speaking-disease come from?

Without thinking too detailed into it, there is no real origin other than communication itself. The spreading of a message, that is the communication and or miscommunication of information can lead to different results.

In Pontypool, the communication of a message lead to spreading where as the miscommunication (changing the meaning) lead to the cure.

The key thing being understanding of English words

A guess could be Montreal, where English-speaking Canadians and French-speaking Canadians reside and how hard it is to interact. Another bigger picture thinking of this could be the willingness to understand or force oneself not to understand what another is saying.

Another idea could be that understanding of a message may not be spontaneous and may plant itself as idea in the minds who listen, without their awareness, e.g. in the case of subliminal messages.

For example, how long it took some of the characters to realize they were infected

Short version: The virus evolved from the dialogue Mazzy gave over the radio, as heard in the opening credits of the movie, and as shown visually as “typo” becomes “Pontypool”. Mazzy is the source and the vector – who spread it over the radio to the local community.

Long version: In the book (originally a radio play) the name of the disease is Acquired Metastructural Pediculosis (AMPS), and is caused by a virus. The author of Pontypool was a linguist, and threw together a bunch of known conditions: (aphasia, phonemic paraphasias, echolalia, semantic paraphasias, anomia, verbal stereotypies, etc.) and associated them with his story’s disease. The interesting twist is that rather than a physical virus (a single strand of genetic information encased within a protein capsule, and transmitted physically) the virus is multivariate strand(s) of non-genetic information transmitted within sound waves. (Although not explicitly mentioned, the term for this is “meme”, or “memetics”, in which the emerging study is named - a branch of metaphysics.)

It’s more complex than a traditional virus, in that it’s not bound - there is no capsule of ‘badness’ that moves from one person to another; it’s not self-contained. The transmitted/received trigger is only a component of the virus, and serves as a key to unlock components already contained within the host. Further – words/sounds themselves have different meanings to different people. So the key for one is not necessarily the key for another. All this leads to seeming inconsistency in how the virus is transmitted and manifests (but the Dr. tells us it always ends up the same.) The puzzle of the story is figuring out how it transmits, and then how to inoculate it.

The notion of it being a terrorist attack on English speaking Canadians (presumably by French speaking Canadians) is supported (at least in the minds of the characters), and it is not insignificant that the Laurel-Ann character fought in Afghanistan – but one way to look at that is to think that within the English speaking people a meme-virus may evolve itself that causes the malfunction. So it can be taken both ways: “someone” is attacking the English speakers – or – the English speakers innately are susceptible to this virus and go crazy in a way that scales up, like an epidemic, leading to war. (i.e. religion – itself a meme complex, and thus religious wars. The studio is, after all, broadcast from an old church.)

The kicker is that the entire story may actually be within a single infected person – a kind of daydream. So all characters are contained within his head – the radio studio. All the things outside (that we never see) are full abstractions. (The story is gloriously polysemous!!)

So where do physical viruses come from? They come from the dawn of life on earth, and in fact may predate cellular life, and have evolved along with us. We need them to survive. Occasionally one mutates and evolves into an epidemic. Same with this memetic virus AMPS.

So just like SARS originated in Chinese bats, who infected civets, who made it to a Chinese food market. I think the Pontypool virus was originated in the opening dialogue of the movie, which was recorded the day before (and played the day before) and was being rebroadcast in the car as Mazzy was driving to work in the early AM. Out of the chaos of that speech – the memetic virus was born. That is my simplistic understanding of “the bigger picture” behind it all that you requested.

(Note: all of this is in complete agreement with @phwd‘s simple first paragraph.)

After going almost completely insane thinking about this movie and trying to solve it, I believe that it is a metaphor. In the beginning, "Mazzy" says "If you piss off enough people, they will eventually become your fans, and that makes other people want to listen because those pissed off people tell other people they know and get them pissed off". Well, killing or murdering someone or committing suicide is a complete bastardization of mankind by God, right? Well, if he is spreading all this negative energy to people... In the end anyway, he says "Kill is Kiss". So in other words, he is telling people the opposite now, that instead of bad being good, good is bad. This in turn corrects the negative energy. The idea for this movie is in some way original. I do not know about other people, but long before I saw this movie, I would get deeply lost in thought trying to repeat a word because it all of the sudden didn't make any sense. Now the whole point of this movie, is to literally screw with your mind. It is just enough, I believe, to make a mentally unstable person to go completely insane if they watch this movie. I almost did. I still feel different. This movie messed with my mind so much, I really could not think of anything, at all, in my brain. I feel like my soul literally got lost in the back of my brain somewhere and could not come out. I couldn't even move my body, not even shut my eyes. I started hearing voices, and seeing things, I was scared of the voices. Then, all of the sudden, like a snap of a finger, it stopped. But my mind still feels half lost in the middle of nowhere. Watching this movie literally made me feel like I did a hallucinogenic drug.

Anyway, in the movie, in the late beginning, apparently only English words are infections - some English words - particularly - anything that involves LOVE. Words like Sweetie, Lovely, Cutie, Lovely, Precious - Turned people into killing machines. Maybe because it is another metaphor for people not ever being able to understand what love is? Also, this movie happens on Valentines Day - Feb. 14 - Hmm... Curious. If Kill is Kiss... and Kiss is kill... think about that Kiss is Kill. Got it now? All the hate bottled up in people is misinterpreted - and when someone says that to love is to kill... the meaning of the word gets jumbled, and they believe that they are supposed to love and kiss, but if they believe now what to kill is to love and kiss, then that is what they will do.

Say, for example, if you took the word breathe. Now think about it hard. Say this word to yourself 20 times. Eventually this word will become unknown to you. In the back of your head, you know what it means, but the definition of the word you are thinking about or saying has been lost. It is alien to you, because you usually do not think about words like that when you say them, you just say them and you leave it be. But when you try to think about what the word you are saying means, you can lose your sense of language, and everything and every word will become unknown. In the movie, just the title of the film itself is a metaphor. Pontypool. What the hell does that mean? Exactly! If you say Pontypool over in your head enough times, it makes absolutely no sense.

"Words lose their meaning when you repeat them them them them them them them them them them them them them them them them them" - If people all over town saw Honey on the cat posters so much:

Honey the Cat - Lost - Friendly and Affectionate. Lost friendly. Lost honey. Lost affectionate. Honey is lost.

If the people in the movie that are supposedly sick with the contaminant, then all the words they are repeating and saying... maybe do not make sense when you think about it. It is a repeating process that they cannot come out of. Another MAJOR point in the movie, is the cat posters. Almost forgot about that didn't you.? Well what could they mean? Well the Cat's name is HONEY. Where are you Honey. Honey. Honey. If everybody in the town went insane from reading the cat posters all around town, then Honey is the first infected word? Maybe the person who put those posters there knew it. Or maybe she already had it from her cat. Maybe the cat spread the virus? Who knows. If Pontypool means Typo, then is Pontypool an error. Is their town bad. Words rooted within other words? Have I lost you yet or jumbled your mind? Have you gone completely insane?

There are a few things that do not make sense still... besides from almost everything (ha) - why only the English language? Why emotion related words? Any words using emotion spreads it if you understand it? Why the cat posters? Could they be metaphors for people losing their loved ones? LOVED ones. If they lose emotion, they lost what makes them human. They cannot handle emotions, and strong words like Love and Darling... I don't know I'm starting to mumble, so I am going to try to stop here.

Anyways tell me what you think? Is it like it is, is there a deeper meaning, is there more than meets the eye, why emotion and love related words, why only the English language, why the cat posters, and why Valentine's Day?

"lurking in the center of Pontypool is the word "typo"?" "The crux of Pontypool is a question of whether mass communication does more harm than good. Mazzy is torn between going off the air to prevent the spread of the virus and using his mouthpiece to warn the citizens of Pontypool of the plague. Mazzy's ego, like the plague itself, won't let him stop talking."

"In the beginning of the movie, the omniscient voices says "Pontypool... Pontypool, PontyPull... PantyPull" This is an example of the metaphor behind the basis of the title itself and also the movie itself.

"I believe that the ending is just there to make a point that you should be confused by events to save yourself from the virus, or that its tongue in cheek that watching the film, you may have picked up the virus and the end bit 'cures' you from your fate, either way, very clever."

"I believe that the initial cursed word was not 'Pontypool' itself, but 'Honey', The Cat named honey, posters all over town with everyone seeing all day, then used again in the French Army broadcast 'Please refrain from using terms of affection such as 'Honey', Sweetheart.. and so on...' and next time you watch it, watch how many times 'Sydney' says the word throughout the film, it must be a good six or seven times!"

I think another point of this movie, is that the American and English media, is turning people into brain-washed, out of control, psychotic people. The American media is so very false and beyond the point of no return when it comes to lying all the time, it is all they do, and people believe them. The American Media is completely false. Nothing they say is the truth. It is very liberal, mainly because of President Barrack Obama, same for the Nazis in World War II. The media is destroying us. We are literally being brainwashed and turning into zombies. I've seen it for myself, even in my family, my aunt. She is completely brainwashed and there is no turning her back. She is a liberal Obamazombie. France and Canada obviously know this is true, and it is, but sadly our own American people cannot figure that out. They think they are being told the truth. George Orwell's 1984 ring a bell here? If the words they are telling them appear to be the truth but are actually not the truth, then this can jumble the meaning, leading them to insanity. In 1984, words are deleted every day not created. Anything to do with knowing the truth is terminated. The only thing the people can do is listen to the lies, even knowing that they are false, they will hear it so much it will become the truth. So lies are now truth. Lie is Truth. Truth is a lie.

'The Other Half is the word. The Other Half is an organism. Word is an organism. The presence of the Other Half is a separate organism attached to your nervous system on an air line of words can now be demonstrated experimentally. One of the most common hallucinations of subject during sense withdrawal is the feeling of another body sprawled through the subject's body at an angle... yes quite an angle it is the Other Half worked quite some years on a symbiotic basis. From symbiosis to parasitism is a short step. The word is now a virus. The flu virus may have once been a healthy lung cell. It is now a parasitic organism that invades and damages the central nervous system. Modern man has lost the option of silence. Try halting sub-vocal speech. Try to achieve even ten seconds of inner silence. You will encounter a resisting organism that forces you to talk. That organism is the word.'

Well from what I watched I realized that the very beginning were Mazzy talks about the lost cat, honey could have contributed to the virus, but what I picked up on was during the interview with Ken someone interrupted and spoke something in French. He simply told them not to translate what has been said and they broadcasted it to everyone that is what contributed to the spreading of the virus the most. Also, because of their many viewers it affected a bunch of people, as Mazzy says "If you piss off enough people, they will eventually become your fans, and that makes other people want to listen because those pissed off people tell other people they know and get them pissed off" Which is exactly what happened, and the virus spreads like any normal virus would.

They pretty much explicitly tell you where the virus comes from. Dr Mendez states that the virus sprang into being from an individual's perception and then calls it a God Bug. This is referring to Schrodigner's Cat which explains how probability waves in higher dimensions are condensed into lower dimensions like ours through individual perception. The virus, being a "God Bug," means it was once in an alternate or higher quantum dimension and somehow became condensed into ours. This does not rule out Mazzy as a vector, however Honey the Cat was definitely involved, perhaps the cat was both alive and dead until Mrs. Du Flaque saw it on the bridge, collapsing the wave function and condensing the virus into the third dimension, just like in Schrodinger's Experiment. I have not however read the book, this is just what I gathered from what was explicitly stated by the characters in the movie.